MRI is an imaging method which excites nuclear spin of an object set in a static magnetic field with a RF (radio frequency) signal having the Larmor frequency magnetically and reconstructs an image based on MR (magnetic resonance) signals generated due to the excitation.
The MRI apparatus is designed so that the systems including the gradient power supply are always in an on-state in order to obtain images of an urgent patient promptly. Specifically, when the driving system of the MRI apparatus starts up, the subsystems including the gradient power supply associated with the driving system become constantly the system ready state.
Furthermore, due to the increase in the speed of imaging for the MR.I apparatus, the maximum output power of the gradient power supply reaches from a few watts to tens of megawatts. The reason why such a large amount of output becomes available is that the output circuit of the gradient power supply is composed of a high-speed switch circuit with a semiconductor.
However, as a disadvantage of the high-speed switch circuit used for the gradient power supply, the problem occurs that there is still a few kilowatts of the power consumption even in the state with no power output. Furthermore, even when it is not being imaged, there is power consumption in the various parts configuring the driving system of the MR.I apparatus as well as the high-speed switch circuit. Therefore, it is desirable to reduce more power consumption for the MRI apparatus.
Accordingly, it is an object of the present invention to provide a magnetic resonance imaging apparatus and a magnetic resonance imaging method which make it possible to reduce the power consumption.